This invention relates generally to a wristwatch of the electronic type and more particularly to a wristwatch where the gear train allows for a thinner overall construction. This is accomplished without shaking or rubbing of the hands. In the prior art there has been a conflict between the thickness of the overall watch and the operating condition of the hands. Generally, the thinner that the watch is made, the more likely it is that the hands will shake or rub together. As a result, thinner gear trains have usually resulted in more space being required between the hands and between the dial and glass in order to prevent rubbing. Accordingly, the overall effect is that the watch is not reduced in thickness. A watch hand will tend to shake if the rotating support member to which it is attached is not aligned and supported along a substantial length. The very small size of these individual components makes it extremely difficult to produce a hand which will not shake when the support member for that hand is short.
In one conventional method for rotatably supporting the center wheel and pinion, the upper tenon is rotatably supported by the train wheel bridge and the lower tenon is rotatably supported by the plate. For purposes of this application, a tenon is a projecting member of a component, this projecting member being inserted for support in another element, generally a plate. The tenon may be a rotating connection between the elements or a fixed connection between the elements, as stated in the following description. In another conventional method, the center wheel and pinion is provided on the backside of the plate and is supported by the support shaft of the center wheel and pinion which is positioned on the plate. In the former method, the thinner the watch becomes, the shorter is the distance between the place where the upper tenon is supported and the place where the lower tenon is supported. As a result shaking of the hands becomes greater. Consequently, it is necessary to provide a wide space between the upper surface of the dial and the lower surface of the glass enclosure, usually known as the crystal, wherein the hands are mounted. Thereby, the watch becomes thicker in spite of the fact that the gear train itself may be thinner.
On the other hand, if the space available for mounting the hands is of conventional height, it is difficult to mount the hands and a problem, namely, a rubbing of the hands one against the other, is likely to occur. In the latter method described above, the center wheel and pinion are arranged on the dial side, or front side, of the plate, then a third wheel pinion is necessary on the front side of the plate. Accordingly, the lower tenon of the third wheel and pinion should be rotatably supported by another member and the plate. Therefore, the range of variation of the central distance from the center wheel to the third wheel pinion becomes larger. The engagement of the wheels is unsettled and the thickness of the watch is not less than the additive thickness of the members. When the lower tenon of the third wheel and pinion is supported by the plate, as is well known in the art, the weight of the hour wheel directly falls on the center wheel and pinion. Thus this gear train design cannot be applied, especially to a gear train for a watch wherein the driving torque is small, for example, an analog quartz crystal watch.
What is needed is a gear train mechanism for a wristwatch which allows for a thin watch and does not cause problems or rubbing or shaking of the hands.